1. Field of the Invention
This invention relates in general to an error correction coding, and more particularly to a packetized trellis coder for error correction coding of Ethernet packets for transmission at one gigabit per second over twisted-pair wiring.
2. Description of Related Art
Gigabit Ethernet promises to breath new life into the Ethernet world by prolonging the life of Ethernet LAN technology into the next century. Gigabit Ethernet is the Ethernet solution for satisfying ever-increasing bandwidth consuming applications at an affordable cost, while complying with Ethernet standards. The existing Ethernet infrastructure is used and promises ease of migration without any changes to existing network operating systems and applications. In July 1996, just five months after the 802.3u Task Force approved standards for fast Ethernet, the IEEE instituted the 802.3z Task Force to define standards for Ethernet operation at one gigabit per second (1.0 Gbps).
The Gigabit Ethernet market will be driven by user needs for faster response times, more segment capacity, and substantial improvements in backbone bandwidth and server performance. Desktop computers are increasing in speed at a rapid rate. The Peripheral Connection Interface (PCI) is the interface of preference because it runs at high speeds. A 32-bit PCI runs at 1.056 Gbps, while the new 64-bit PCI doubles that speed. Also, workstation and server performances are advancing, enabling these devices to flood multiple fast Ethernet links with network traffic.
Gigabit Ethernet technology is not simply an upgraded version of Ethernet or fast Ethernet. Nevertheless, Gigabit Ethernet will be inter-operable with both technologies and preserve the fundamental precepts of standard Ethernet framing. Gigabit Ethernet will also comply with the 802.3 standard for frame format and minimum and maximum frame size. However, the physical layer will be different.
Like fast Ethernet, Gigabit Ethernet operates in either half- or full-duplex mode. In full-duplex mode, packets travel in both directions simultaneously over two paths on the same connection for an aggregate bandwidth of double that of half-duplex operation. For example, a full-duplex fast Ethernet connection provides an aggregate bandwidth of 200 Mbps, while a full-duplex Gigabit Ethernet connection yields an aggregate of 2.0 Gbps. Full-duplex transmission can be used for point-to-point connections only. Since full-duplex connections cannot be shared, collisions are eliminated, and the CSMA/CD access control mechanism is disabled. Full-duplex transmission can be deployed between ports on two switches, a server or workstation and a switch port, or between two workstations. Full-duplex connections cannot be used for shared-port connections, such as a repeater or hub port that connects multiple workstations.
An optional flow-control mechanism, presently being defined by the 802.3x Task Force, is available for full-duplex transmission and is similar to XON/XOFF flow control. A receiving station at one end of a point-to-point link sends a packet to the sending station instructing the sending station to halt packet transmission for a specified period of time. The sending station ceases packet transmission until the time interval is past or until it receives a new packet from the receiving station with a time interval of zero. It then resumes packet transmission.
For half-duplex operation, Gigabit Ethernet will retain the standard Ethernet CSMA/CD access method. Half-duplex operation is intended for shared multi-station LANs, where two or more end stations share a single port. Most switches enable users to select half- or full-duplex operation on a port-by-port basis, allowing users to migrate from shared segments to point-to-point, full-duplex segments when they are ready. Gigabit Ethernet is most effective when running in the full-duplex, point-to-point mode where full bandwidth is dedicated between the two points. Full-duplex operation is ideal for backbones and high-speed server or router links. In half-duplex mode, Gigabit Ethernet's performance is degraded. It is sensitive to segment length because it uses the CSMA/CD protocol. The standard slot time for Ethernet frames is not long enough to run a 100-meter cable when passing 64-byte frames at gigabit speed. In order to accommodate the short-frame timing problems experienced with CSMA/CD when scaling half-duplex Ethernet to gigabit speed, slot time has been extended to guarantee at least a 512-byte slot time using a technique called carrier extension. The frame size is not changed; only the timing is extended.
The vendor community, through the Gigabit Ethernet Alliance, is promoting Gigabit Ethernet as the technology of choice for high-performance solutions on Ethernet LANs. Gigabit Ethernet is a more attractive alternative than ATM in terms of price and ease of migration, but without the functionality of ATM. Although Gigabit Ethernet will satisfy high-performance needs for data, it may not provide the quality of service that is necessary for high-quality multimedia applications. Unless the quality of service can be improved, delay-sensitive applications, such as video and voice, will not approach the quality provided by ATM. Further, copper media operating at these speeds presents inherent reliability problems.
While ATM is a highly scaleable, multimedia transport technology, Ethernet is primarily intended for data applications and its scaleability is limited. Thus, the window of opportunity for Gigabit Ethernet will undoubtedly be impacted as ATM deployment scales upward and ATM prices continue to decline. Nevertheless Gigabit Ethernet offers the performance needed to satisfy intensive traffic congestion and bandwidth-hungry data applications.
To improve bit error probability, coding techniques have been used extensively in communication systems. For example, block codes and convolutional codes have been used to improve bit error probability by bandwidth expansion. Bandwidth is increased by replacing each k-tuple message with an n-tuple codeword, where n&gt;k. However, bandwidth expansion is not possible with bandlimited channels. Still, combined modulation and coding schemes have been developed to achieve coding gain without any bandwidth expansion. Due to the availability of Viterbi decoders , trellis coding is one of the more popular coding schemes. Nevertheless, trellis codes have been applied to data transmission systems without regard to the packetized or non-packetized nature of the data.
Thus, it can be seen that there is a need for a reliable method for achieving Gigabit Ethernet frame format data transmission using twisted pair wiring.
It can also be seen that there is a need to provide error correction coding of IEEE 802.3 frame formatted Ethernet packets over twisted pair wiring.